Can’t complete tasks

I’m not sure if I’m doing something wrong, but every so often I can’t check off a task (“complete an action”) on the Mac. The circle turns yellow momentarily when I click on it, but then it goes back to normal, with no checkmark. I’ve tried syncing, quitting and relaunching, and just clicking over and over. Nothing seems to work, except for switching over to the iOS app, checking it off there, and syncing.

Am I doing something wrong, or is this just a really obnoxious bug (one that requires you own a separate version of the software just to complete a task!)?

Perhaps a long shot, but: is it a repeating action? It sounds like the behaviour that occurs when an action repeats and is available immediately.